According to one Texas dental interviewed: 13 million Americans who brush in the shower are wrong.

“Dr. Benjamin Johnson, founder of Acre Wood Dental in Waco, Texas, advises his patients with poor dental health not to brush in the shower partly because it could lead to flaws in brushing technique. Without a mirror, he says, it’s easier to get the angle wrong, and the shower can make brushers so relaxed they miss spots. Besides, he says, you are more likely to drop your toothbrush in the shower.

When his patients protest, Dr. Johnson pulls up their dental X-rays and points to their teeth. “We like to talk about patients doing habits that are good for them, and showering with the toothbrush is not good for you,” he says.”